AACMMs have found widespread use in the manufacturing of parts where there is a need to rapidly and accurately verify the dimensions of the part during various stages of the manufacturing (e.g., machining) of the part. Portable AACMMs represent a vast improvement over known stationary or fixed, cost-intensive and relatively difficult to use measurement installations, particularly in the amount of time it takes to perform dimensional measurements of relatively complex parts. Typically, a user of a portable AACMM simply guides a probe along the surface of the part or object to be measured. The measurement data are then recorded and provided to the user. In some cases, the data are provided to the user in visual form, for example, three-dimensional (3-D) form on a computer screen. In other cases, the data are provided to the user in numeric form, for example when measuring the diameter of a hole, the text “Diameter=1.0034” is displayed on a computer screen.
Measurements by an AACMM of the three-dimensional (3D) physical characteristics of surfaces of objects may be carried out with contact and non-contact probes for a variety of reasons, including part inspection, rapid prototyping, comparison of the actual part to a CAD model of the part, reverse engineering, 3D modeling, etc. Most often, non-contact devices use triangulation-based techniques to process the raw captured data to obtain 3D coordinates of surface points.
One type of triangulation-based, non-contact device is a laser line probe (LLP), which includes a projector and a camera. The projector includes a light source that emits a light, typically as a line. Thus, the LLP is also known as a line scanner. The emitted light may be laser light, partially coherent light, or incoherent light. The camera includes a camera-type imaging device, such as a charge-coupled device (CCD) or CMOS photosensitive array. The camera captures the pattern of light on the object surface, which is processed to determine 3D coordinates of an object surface.
Another type of triangulation-based, non-contact device that includes a projector and a camera is an area scanner, also known as a structured-light scanner. In such a scanner, the projector projects onto a surface a two-dimensional pattern that is captured by the camera and processed to determine 3D coordinates.
An example of a prior art portable AACMM is disclosed in commonly assigned U.S. Pat. No. 5,402,582 ('582), which is incorporated herein by reference in its entirety. The '582 patent discloses a 3D measuring system comprised of a manually-operated AACMM having a support base on one end and a “hard” measurement probe at the other end. Commonly assigned U.S. Pat. No. 5,611,147 ('147), which is incorporated herein by reference in its entirety, discloses a similar AACMM. In the '147 patent, the articulated arm CMM includes a number of features including an additional rotational axis at the probe end, thereby providing for an arm with either a two-two-two or a two-two-three axis configuration (the latter case being a seven axis arm).
It is generally known to attach an LLP to the probe end of an AACMM. The result is a fully integrated, portable, contact/non-contact measurement device. That is, the AACMM having an LLP attached thereto provides for both contact measurements of an object through use of the hard probe of the AACMM and for non-contact measurements of the object through use of the LLP's laser and imaging device. More specifically, the combination AACMM and LLP allows users to quickly inspect or reverse engineer complex and organic shapes via laser scanning, as well as to capture prismatic elements with the relatively high accuracy that contact metrology provides.
When combined as such, the AACMM and LLP may have the LLP carry out some or all of the processing of the 3D captured point cloud data using the signal processing electronics (e.g., computer or processor) within or associated with (e.g., located apart from) the AACMM. However, the LLP may have its own signal processing electronics located within the LLP or associated with the LLP (e.g., a stand-alone computer) to perform signal processing. In this case, the LLP may connect with a display device to view the captured data representing the object.
It is known to disconnect an area scanner from an AACMM for handheld operation. Usually, such handheld operation is limited to capturing a line of light or pattern of light in a single shot. In such handheld operation, 3D coordinates of surface points over large areas are obtained by registering together multiple 3D images, usually by matching common image features such as edges or holes. With this method, a relatively large object measured in several scans may provide a single large collection of 3D surface coordinates.
A difficulty with this registration method may arise when an object being scanned has relatively few features. In such a case, a flat surface may be registered in a warped shape. In addition, although it is possible to use an area scanner removed from an AACMM in a handheld mode, it has not generally been possible to use an LLP in a handheld mode as a collection of single lines. A potential difficulty is that the collecting of multiple lines may not provide enough information to permit multiple line-scans to be fit together over a two-dimension surface area. Consequently, improvements are desired for methods of using a handheld LLP or area scanner to obtain a relatively accurate 3D representation over a relatively large area.
While existing line scanners and area scanners are suitable for their intended purposes, what is needed is a handheld scanner having improved registration over relatively large regions. What is further needed is for such a handheld scanner to be further useable with an AACMM.